Federal safety regulators who have been examining the safety of DaimlerChrysler Corp. minivan passenger-side air bags decided yesterday not to open a formal investigation into why the safety devices have caused the deaths of 12 children, according to sources close to the study.

Based on its examination of accident reports, the National Highway Traffic Safety Administration found that when it considers the number of DaimlerChrysler minivans on the road and the length of time they have been on the road, the number of deaths of infants and children is not out of line compared with other vehicles.

The agency, which has scheduled a briefing today, plans to continue to examine injuries and fatalities in DaimlerChrysler minivans, comparing accident results with laboratory tests performed with dummies.

Chrysler was the first manufacturer to introduce passenger-side air bags in its minivans in 1994. Its highest rate of child fatalities due to air bags occurred in the 1994 and 1995 model years; the number declined after 1996, when the minivan was redesigned and a nationwide effort was launched to teach parents to buckle children in the back seat. In 1997, the company began installing a less forceful air bag as a replacement part in its minivans.

The agency announced last March that, based on tests performed with dummies, it had concerns about severe head and neck injuries that a petite female or a child might sustain if hit by an air bag while riding in the front seat of a DaimlerChrysler minivan.

Since then, DaimlerChrysler has been working to convince the agency that when a statistical analysis is performed of injuries and deaths due to passenger-side air bags in all vehicles -- adjusting for factors such as a higher likelihood that a child will be seated in the front seat in a minivan -- there is no reason to further investigate DaimlerChrysler.

Michael Aberlich, spokesman for DaimlerChrysler, said it looked as if NHTSA "has done what we've asked them to do -- look at this globally."

"If you look at all minivans from 1994 to 1997, our analysis says there are 35 other nameplates with higher fatality rates than our Chrysler minivans," he said.

DaimlerChrysler's case also may have been bolstered by the agency's probing of 35 other air-bag-related fatalities, which include deaths in minivans other than those made by DaimlerChrysler -- a finding NHTSA is expected to discuss in its briefing today. Until recently, DaimlerChrysler was the only minivan manufacturer to suffer passenger-side child fatalities.

Before this research effort, the Center for Auto Safety petitioned the agency in 1996 asking for a formal investigation. The agency denied the petition.